The present invention relates to propulsion regulation in motor vehicles in the sense of a reduction of the undesired slippage of the driven vehicle wheels, with a regulating circuit responding to the movement condition of at least one driven wheel which, in case of a tendency to slip on the part of this wheel, effects a reduction of the output torque of the drive aggregate.
An installation of this type is known from the DE-PS No. 31 27 302.
In such installations known as drive slippage regulation-DSR-the brakes of one or both driven wheels are actuated upon a determination of a slippage tendency (when a regulating magnitude exceeds a threshold value) of at least one driven wheel, or a magnitude determining the output torque of the driving aggregate (fuel injection quantity or throttle valve opening angle) is reduced with a predetermined adjusting velocity until the monitored regulating magnitude again drops below the threshold value whereupon the brakes are released and, for example, the throttle valve angle is again increased with predetermined adjusting velocity.
The time delay between the adjustment of the throttle valve and the reaction of the engine which amounts approximately to 200 ms, causes undesirable regulation action on the driving torque. This time delay becomes particularly disadvantageous with a drive slippage regulation that regulates exclusively the driving torque and does not dispose of a "fast regulating circuit" acting on the wheel brakes. In this case there is no assurance that the engine torque can be matched optimally and sufficiently quickly to the requirements by adjustment of the throttle valve such, in order to avoid an excessively large regulating deviation.
It is the object of the present invention to improve the regulation of the magnitude determining the output torque of the drive aggregate that during the regulation of a driven wheel as small as possible an excess torque both in the positive as also in the negative terminal phase of the regulating cycle occurs at this wheel.
The underlying problems are solved according to the present invention in that the regulating circuit is so constructed hat the instantaneous value of the magnitude determining the output torque is stored and the magnitude itself is reduced to its minimum value if a value coordinated to the velocity of a driven wheel exceeds the threshold value coordinated to the vehicle velocity thus the magnitude is brought to a value which is smaller than the instantaneous value stored in the respective regulating cycle by a value dependent: on the stored instantaneous value, on the engine rotational speed, on the ratio of the engine rotational speed to the rotational speed of the driven wheel and on the maximum value of the wheel acceleration that has occurred since exceeding the threshold value coordinated to the vehicle velocity, if the acceleration of the driven wheel passes over into a deceleration, and in that the magnitude is increased to a value which is greater than the value previously kept constant by an amount dependent: on the stored instantaneous value, on the engine rotational speed, on the ratio of the engine rotational speed to the rotational speed of the driven wheel and on the maximum value of the wheel deceleration that has occurred since the beginning of the wheel deceleration, if the value coordinated to the velocity of the driven wheel drops below the threshold value coordinated to the vehicle velocity.
The advantage of this method according to the present invention resides in the regulation of the excess driving torque which is proportional to the acceleration of the wheel under consideration.
After a complete regulation of the engine torque to the idling limit (idling rotational speed) of the engine during the beginning of regulation, i.e., when the driven wheel exceeds, for example, a slippage threshold, the engine torque is increased to a value coordinated to the measured maximum wheel acceleration when the wheel acceleration disappears as a result of the regulation, i.e., passes over into a deceleration. In this manner, the driving torque can be corrected more rapidly and more exactly during the acceleration phase. The excess engine driving torque is reduced corresponding to the measured maximum acceleration during the first phase of the regulating cycle which is characterized by a slippage increase, by way of the engine performance graph (set of characteristic curves) and in the second phase of the regulating cycle (slippage decrease) a slight excess in friction torque transmitted from the tire is effective. The following movement equation of the wheel is valid as calculation basis: ##EQU1## wherein .omega. is the circumferential acceleration of the wheel,
M.sub.M is the engine torque, PA1 M.sub.R is the friction torque, and PA1 .THETA. is the inertia moment.
The further regulation in the deceleration phase of the wheel takes place in a similar manner so that altogether a small regulating deviation occurs in the following regulating cycle. Also in this case, the maximum value of the negative acceleration is evaluated for the increase of the driving torque as soon as the first regulating cycle is terminated.
The regulation can be optimized by taking into consideration longitudinal and cross acceleration signals(steering angle signals) depending on requirements as regards more traction or stability.
More stability is attainable if the engine torque is reduced more strongly on the basis of the measured acceleration values and subsequently, after the regulating magnitude has fallen below the threshold value, is increased, not immediately but with time delay. As a result thereof, the vehicle is able to stabilize which is of advantage in particular in a curve after a sudden depression of the gas pedal, (kick-down).